Piston pumps may be used to deliver and/or recirculate viscous media having a high proportion of solids (suspensions) at high pressures of greater than 200 bar and high temperatures of greater than 300° C. However, they are only suitable in a limited way for an application of this type, because the solid components destroy associated seals of a piston in a relatively short time and cause scoring on a surface of the piston.
A possibility for avoiding these difficulties is to use diaphragm pumps. To implement delivery at the above-mentioned pressures, only designs having hydraulically driven diaphragms may be used. In turn, these may only be conceived for secure and interference-free operation in the cited temperature range with significant design and material technology outlay.
The use of plastic diaphragms made of PTFE, for example, is not possible, because plastic begins to flow significantly at the cited high pressure and high temperature. The use of metal diaphragms is possible in principle, but technical demands such as multilayered diaphragms having fracture signaling and an embodiment as a diaphragm oscillating freely in the product space having position control may only be implemented with great effort, see EP 0 085 725 A1.
Up to this point, pumps having a so-called remote valve head have been used as a measure against the high temperature strain. In such a design, a diaphragm pump operates as an upstream pulsator, which actuates the operating valve in the downstream remote valve head of the pump with the aid of the fluid to be delivered via a pipeline acting as a cooling line. In this way, the diaphragm pump may operate in the noncritical low temperature range up to approximately 150° C. However, it is disadvantageous that possible solid components of the fluid to be delivered may clog the pipeline between the upstream pulsator and the remote valve head and thus impair the delivery effect.
The high pressure of the fluid to be delivered results in a further problem. The piston rod force of oscillating displacement pumps, which results from the product of pressure and area, requires the use of very large pump drive assemblies in certain circumstances, which may be uneconomical in two regards for the required application. Firstly, significantly higher investment costs and secondly higher life cycle costs are connected thereto, which may be particularly distinguished by energy costs and outlay for wearing and replacement parts. The economic consideration of pump systems for recirculation having the boundary conditions cited above is especially of very great significance in methods for energy reclamation from biological wastes.